Robert Haas

Tuesday, January 30, 2018

What if PostgreSQL didn’t need VACUUM at all? This seems hard to imagine. After all, PostgreSQL uses multi-version concurrency control (MVCC), and if you create multiple versions of rows, you have to eventually get rid of the row versions somehow. In PostgreSQL, VACUUM is in charge of making sure that happens, and the autovacuum process is in charge of making sure that happens soon enough. Yet, other schemes are possible, as shown by the fact that
not all relational databases handle MVCC in the same way, and there are reasons to believe that PostgreSQL could benefit significantly from adopting a new approach. In fact, many of my colleagues at EnterpriseDB are busy implementing a new approach, and today I’d like to tell you a little bit about what we’re doing and why we’re doing it.

Friday, January 05, 2018

In a recent blog post, I talked about why every system that implements MVCC needs some scheme for removing old row versions, and how VACUUM meets that need for PostgreSQL. In this post, I’d like to examine the history of VACUUM improvements in recent years, the state of VACUUM as it exists in PostgreSQL today, and how it might be improved in the future.

Monday, December 18, 2017

Experienced PostgreSQL users and developers rattle off the terms “MVCC” and “VACUUM” as if everyone should know what they are and how they work, but in fact many people don’t. This blog post is my attempt to explain what MVCC is and why PostgreSQL uses it, what VACUUM is and how it works, and why we need VACUUM to implement MVCC. In addition, I’ll include a few useful links for further reading for those who may want to know more.

Tuesday, September 26, 2017

Since I just committed the last pending patch to improve hash indexes to PostgreSQL 11, and since most of the improvements to hash indexes were committed to PostgreSQL 10 which is expected to be released next week, it seems like a good time for a brief review of all the work that has been done over the last 18 months or so. Prior to version 10, hash indexes didn't perform well under concurrency, lacked write-ahead logging and thus were not safe in the face either of crashes or of replication, and were in various other ways second-class citizens. In PostgreSQL 10, this is largely fixed.

Monday, August 14, 2017

The reaction to the new table partitioning feature in PostgreSQL 10 has been overwhelmingly positive, but a number of people have already astutely observed that there is plenty of room for improvement. PostgreSQL 10, already at beta3, will go GA some time in the next month or two, and presumably once it does, more people will try out the new feature and find things they would like to see improved. The good news is that there is already a substantial list of people, many of them my colleagues at EnterpriseDB, working on various improvements. The following list of projects is complete to my knowledge, but of course there may be projects of which I'm unaware especially at companies where I don't work. If you're working on something else, please leave a comment about it!

Wednesday, April 26, 2017

In a talk which I gave at PGCONF.IN and, in a shorter version, at PGCONF.US, I had a few slides on who contributes to PostgreSQL development. Here, I'd like to present a slightly expanded version of the information which was in the talk. The information in this post considers calendar year 2016 and comes from two sources.

Saturday, April 08, 2017

The list of new features coming in PostgreSQL 10 is extremely impressive. I've been involved in the PostgreSQL project since the 8.4 release cycle (2008-2009), and I've never seen anything like this. Many people have already blogged about these features elsewhere; my purpose here is just to bring together a list of the features that, in my opinion, are the biggest new things that we can expect to see in PostgreSQL 10. [Disclaimers: (1) Other people may have different opinions. (2) It is not impossible that some patches could be reverted prior to release. (3) The list below represents the work of the entire PostgreSQL community, not specifically me or EnterpriseDB, and I have no intention of taking credit for anyone else's work.]